Reamer size for Pressure Plate Dowels on OE Flat Flywheel

[tjanson]

I am going to redrill a flat flywheel for a 240mm 850R clutch to use in a M90 swap into my 245. It requires 3 m6 dowels. I am not sure what reamer size I should use for the dowel holes.

My research indicates in cast iron a "light press fit" with an H7 reamer is appropriate. That means a reamer producing a 6.0-6.012 mm hole with a "standard" m6 M6 dowel 6.004-6.012 mm.

Looking at it "imperially", closest equivalent is a 0.2360" reamer which would make a 0.2360-0.2362" hole for a 0.2364-0.2367" dowel. The .2360 is a little more straight forward for me to source via McMaster than a metric H7 reamer.

What say you, send it with the 0.2360"? Is that too loose?

P.S. / FYI - 240mm 850R pressure plate bolt pattern / circle info
Volvo clutch kit PN 272218
267mm BCD
3x M6 dowels at 0, 120, 240 degrees per Sachs/ZF customer service
6x M8 taps at 30, 90, 150, 210, 270, 330 degrees - measured myself, using caliper measurements to triangulate locations.

 

[crogthomas]

0.2360" = 5.9944mm.
An interference fit is usually slightly smaller than the dowel, so that seems about right to me, but look up the correct figures.

 

[Sjeng]

If the holes turn out too loose, glue them in with loctite 638 or similar.

 

[cwdodson88]

Use a 6mm reamer, and drill with a large diameter drill. Spin reamer slow for tighter fit. Faster for looser fit.

 

[cwdodson88]

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

 

[tjanson]

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

Thanks - I was looking at that one and thinking it was a bit to big at 6.000-6.005 mm. Worst case loose by 0.001 mm. Not the case in your experience?

 

[tjanson]

Getting anxious that this clapped out Bridgeport can't hold position for 3 dowels. I figure drilling out the 3rd pressure plate hole is an option if it doesn't fit. I'll do a test run on a piece of steel and see what happens. I did figure out how to calibrate the DRO and now have it reading dead on over 5" instead of 0.002" off.

 

[sbabbs]

I am curious to see if a 850r 240mm pressure plate can even bolt onto a stock volvo flat flywheel without bolt holes being drilled into the ring gear? Will it even fit? Why not buy the billet steel one from england that is made for 850r clutch setup and m90? I had one, sold it though. I know you can't use it with a M46 as it hits the inside of the bellhousing. The 850r pressure plate that is.

Volvo B230 M90 T5 850R 240mm Lite – TTV Racing

www.ttvracing.com

 

[cwdodson88]

The range is dependent on how much meat the reamer is trying to chew and how fast. This will determine how much deflection in the flute, changing the size. So larger drill, 5.9mm? And slow spindle, small hole. If you need to open it up, use a piece of paper or t shirt and turn the spindle up a tad.

 

[tjanson]

I am curious to see if a 850r 240mm pressure plate can even bolt onto a stock volvo flat flywheel without bolt holes being drilled into the ring gear? Will it even fit? Why not buy the billet steel one from england that is made for 850r clutch setup and m90? I had one, sold it though. I know you can't use it with a M46 as it hits the inside of the bellhousing. The 850r pressure plate that is.

Volvo B230 M90 T5 850R 240mm Lite – TTV Racing

www.ttvracing.com

It's a good point. To be honest I can't remember if I put 850R pressure on flywheel to see if it fit within. It's been modified already with the LH2.4 trigger pattern so there is even less available space. I need to find where I stashed that flywheel and try it out.

The TTV flywheel seems too light for a daily driver type car... what do you think? And it would probably be $800-900 once imported.

Honestly if I hadn't bought the 850 R clutch kit a few years ago I would probably use a dogdish + 940 clutch.

 

[shoestring]

It's a good point. To be honest I can't remember if I put 850R pressure on flywheel to see if it fit within. It's been modified already with the LH2.4 trigger pattern so there is even less available space. I need to find where I stashed that flywheel and try it out.

The TTV flywheel seems too light for a daily driver type car... what do you think? And it would probably be $800-900 once imported.

Honestly if I hadn't bought the 850 R clutch kit a few years ago I would probably use a dogdish + 940 clutch.

I think the reciprocating assembly is heavy enough that it's not a concern.

 

[tjanson]

@sbabbs
You are correct. the M8 taps, and M6 dowels, break into the ring gear if drilled all the way thru. There is also very little clearance to the 60-2 pattern. The M8 taps are ~2 mm to the trigger pockets and the dowels are 3mm when centered between the pockets. Trigger pockets are 8.8 mm deep and thickness to the ring gear is 14.2mm.
Seems marginal. Not sure how I want to proceed.

 

[cwdodson88]

Ideally with an m8 you want 2x dia in thread depth. Too shallow and it may not hold the torque of the fasteners

 

[sbabbs]

With my other m90 I am putting in my SE I have the johnV billet steel flywheel with 2.4 holes that uses 240mm saab areo 9000 pressure plate. His billet steel flywheels use stock volvo ring gear. Saab plate I guess is a wee bit smaller circle wise. The TTV billet one the ring gear is also part of the billet steel flywheel and is not removable. I'd look into seeing how much to get the TTV one or see if someone already has one they will sell you. I sold the one I had with another M90 I had myself..

 

[JW240]

Looks good!

Side note the TTV flywheel (5kg) with 850R clutch works fine for a daily setup. It's not as smooth and Turkey als a stock setup. Still perfectly fine as far as I am concerned.

 

[tjanson]

Looks good!

As in the dowel / tap locations look good?

I could get 12-13 mm thread engagement which is 1,5x diameter. I think that is sufficient. Torque spec is 25 ft-lb. I'd have to remove the ring gear to do the machining. Or I could drill and tap right through the ring gear/flywheel seam and get the full thickness. Seems wrong but I can't think of why not.

I am convinced now the TTV flywheel would be fine on a dd. I am trying to find out what tarriffs would be. Google indicates it might be 25-50% .

 

[cwdodson88]

If it were me, I’d go for it. Worst case you have to buy the new one.

 

[culberro]

As in the dowel / tap locations look good?

I could get 12-13 mm thread engagement which is 1,5x diameter. I think that is sufficient. Torque spec is 25 ft-lb. I'd have to remove the ring gear to do the machining. Or I could drill and tap right through the ring gear/flywheel seam and get the full thickness. Seems wrong but I can't think of why not.

I am convinced now the TTV flywheel would be fine on a dd. I am trying to find out what tarriffs would be. Google indicates it might be 25-50% .

It'll be fine. 1.5x diameter is also OK. At ~8 threads of engagement you'll be at the spot where the fastener or the threaded material could fail. Might by closer to the fastener failing.
I'd suggest removing the starter ring gear before proceeding.

Ideally with an m8 you want 2x dia in thread depth. Too shallow and it may not hold the torque of the fasteners

For mild steel and a gr5 fastener, with 6 full threads of engagement you have thread and fastener strength being equal. For 6061-t6 that's ~10 threads of engagement. Cast iron is ~8 threads of engagement. This rule of thumb has served me very well in my years of design/engineering.

 

[JW240]

As in the dowel / tap locations look good?

I could get 12-13 mm thread engagement which is 1,5x diameter. I think that is sufficient. Torque spec is 25 ft-lb. I'd have to remove the ring gear to do the machining. Or I could drill and tap right through the ring gear/flywheel seam and get the full thickness. Seems wrong but I can't think of why not.

I am convinced now the TTV flywheel would be fine on a dd. I am trying to find out what tarriffs would be. Google indicates it might be 25-50% .

I checked the din/iso standard at work and 1,5x diameter is perfect for 8.8 in cast iron.
The import of such a part is expensive indeed, sadly. It was more a data point on how a 5kg flywheel would work for a DD, and we agree that it is fine.

 

[tjanson]

Over the weekend I put in the dowel and bolt pattern. It fits!

For the record, 5.8mm drill, then 6mm / .2362" reamer @ 630 RPM, plunge, turn off spindle, retract, worked great. I ended up with a fit that could be installed with light taps from a small ball pein hammer, and removeable with vise grips.

The ring gear came off easily with a few minutes of MAP-Pro gas, and a curved drift fashioned from a piece of .25x1.5" steel bar stock.

I calibrated the mill's DRO over 5" with gage blocks and test indicator. I did a test dowel pattern in a Subaru Outback brake rotor and the pressure plate fit great so I proceeded to the real thing. 3 dowels, 6 M8 taps, and many, many tool changes.

Now that the pressure plate can bolt up, I need to cut a recess on the ID of the flywheel friction surface to fit the larger hub of the friction disk. Luckily the flywheel fits on the lathe, but I will have to make a mandrel to hold it.